There is a need in the art for new liquid crystalline polymers. Such polymers must have a working temperature for melt processing before the onset of degradation. Desirably, such polymers would also have good thermomechanical properties, high flame resistance, and good processability.
Liquid crystalline polyesters generally require linear aromatic monomers, e.g., 1,4-aromatic carbocyclic ring systems or 4,4′-biphenylenes, and/or comonomers to reduce the glass and isotropic transition temperatures below the degradation temperature of the polymer, and thus their syntheses can be complicated. For example, U.S. Pat. No. 4,118,372 discloses an anisotropic (co)polyester made from chlorohydroquinone diacetate, terephthalic acid, and 4,4′-bibenzoic acid.
Aromatic polyesters where the aromatic diacid component is isophthalic acid, terephthalic acid, or naphthalene dicarboxylic acid, have only produced semi-crystalline polymers or polymers with transition temperatures above the polymer degradation temperature, e.g., poly(p-phenylene terephthalate) and poly(p-hydroxybenzoic acid) melt above 600° C. These polymers typically require three, four or more comonomers to achieve heat resistance and a melting temperature range suitable for processing. For example, U.S. Pat. Nos. 5,110,896, 5,250,654, 5,397,502, and 6,656,386 disclose liquid crystalline polymers made from several comonomers derived from hydroquinone, 4,4′-dihydroxybiphenyl, terephthalic acid, 2,6-naphthalenedicarboxylic acid, 4,4′-bibenzoic acid, 4-hydroxybenzoic acid, isophthalic acid, 3,4′-bibenzoic acid, etc.
There is thus a need for new aromatic liquid crystalline polyesters that do not necessarily require the presence of comonomers, and/or that have a reduced or no comonomer content, to achieve heat resistance and/or a melting temperature range that may facilitate a commercial manufacturing process, and/or for a simplified method to make and/or process liquid crystalline polyesters.